This invention generally relates to passive radar decoys and more particularly to a self-inflated aerodynamic body incorporating a unique RF retroreflective configuration for radar target enhancement and a packaged body concept for rapid chaff deployment and improved radar cross section.
The use of chaff to defeat the radar function by denying it range and direction (azimuth and elevation) information is a well known and practiced technique in the art of radar jamming and/or countermeasures. Passive chaff elements in the form of discrete dipoles are dispensed by an aircraft to form a distinct cloud which creates a credible false target to the ground-based radar. The dipoles are generally low mass slivers of metallized milar, glass or other suitable dialectric material and these are very compactly and densely packaged into canisters and loaded into ejection equipment aboard the aircraft. The ejection equipment fire the chaff out of the canisters into the aircraft windstream where vehicle-induced turbulence or wind shear effects are available for cloud dispersion. The low mass chaff slivers, upon ejection, rapidly slow down and fall at an almost constant rate. For example, a widely used one mil metallized glass chaff has a settling rate of about 50 feet per minute.
One of the problems with present chaff systems is that the low mass slivers are easily damaged by the high compressive force necessary to eject them from the canister and into the aircraft windstream. Being compressed, the chaff dipoles may not uniformly disperse in the windstream and will therefor not provide the desired radar countermeasures performance.
Another problem with present chaff systems is the fact that the low mass slivers rapidly slow down upon ejection and therefor the useful life is shortened for lack of a doppler frequency return to the radar. The radar can therefore update its return information and easily determine the location of the aircraft because of its doppler velocity.
It is therefor in accordance with one aspect of the present invention, an object to provide a highly effective false target for enhancement of radar target cross section while requiring fewer numbers of packaged chaff elements.
It is in accordance with another aspect of the invention, an object to provide a self-inflated, passive radar decoy that achieves coverage at millimeter wave frequencies and improved chaff dispersion upon ejection from the aircraft and which provides an increased period of doppler frequency return to a ground-based radar.
In accordance with still another aspect of the invention, it is an object to provide a ram-air inflated passive decoy that has a unique RF retroreflective configuration for millimeter wave radar target performance.
The various aspects and advantages of the invention are met in a passive radar decoy comprising a substantially hemispherical upper body portion having an inner surface coated with an RF reflective material; a weighted nose piece; a tapered lower body portion interconnecting the upper body to the nose piece; and means to ram-air inflate the decoy when it is released from the aircraft such that RF energy impinging on the hemispherical upper body is reflected back to the source of RF energy.
Other aspects and advantages of the invention are met in a configuration for a radar countermeasures package for deployment from an aircraft in flight having a radar countermeasures system including an ejection tube having a force driven piston therein to effect expulsion of the contents of the tube into the atmosphere in response to a radar countermeasures requirement comprising a segmented tube mounted coaxially within the ejection tube; a passive radar decoy having a weighted nose piece and a ram-air inflatable body, the inner surface of the body coated with an RF reflective material and said inflatable body packaged within the segmented tube; and a plurality of chaff dipoles positioned within the ejection tube between it and the segmented tube, said segmented tube, passive decoy, and chaff dipoles being expelled from the ejection tube by the force-driven piston.